1. Field of the Invention
The present invention relates to fermentation processes and processes for the production of yeast, and particularly to a method of producing baker's yeast that uses date syrup as part of the substrate.
2. Description of the Related Art
The economic utilization of dates is a very important issue to the Kingdom of Saudi Arabia because this crop is the most important agricultural produce of the country. The date crop is also the historical staple in the whole area, having a very high religious and cultural significance, which makes the continuation of its production at the highest possible levels a national priority. Thus, Saudi Arabia is one of the major date producers in the world, with an annual production of about one million tons of date fruits. About 50% of this amount is consumed locally as human food, 4% exported and 4% used as animal feed. More than 40% of the annual produce, i.e., about 400 thousand tons, mainly fruits of the low quality Rezez variety, represents a surplus for which there is currently no economic use. Rezez is produced in large quantities because the tree can grow in marginal soils without much need for fertilization, but still gives high yields of fruits.
Baker's yeast is a type of yeast used in the production of leavened bread, cakes, pastries, and other bakery products. Baker's yeast converts the fermentable sugars in dough into carbon dioxide and ethanol. The most common strain of yeast in baker's yeast is Saccharomyces cerevisiae, which is also used in fermentation processes for the production of alcoholic beverages. Baker's yeast may be processed so that it is available to the user in a variety of forms, including dry yeast (which may be in cakes or in granules) and liquid yeast, and in active or dehydrated forms.
Baker's yeast can be produced from substrates that contain metabolizable sources of carbon, energy, nitrogen, minerals and essential vitamins. Substrates that contain carbon and energy sources readily metabolizable for Saccharomyces cerevisiae can be directly used for production of baker's yeast, while those containing complex carbohydrates, such as starches in grains and cellulose in green or woody plants, need costly hydrolytic treatment before use. The substrate of choice for baker's yeast production in the world today is molasses derived from beets or sugar cane.
Saudi Arabia imports all of its local market needs for baker's yeast, which amounts to about 10 thousand tons per year. A factory for the production of baker's yeast that was based in the city of Jeddah, in the west of the country, stopped production, partly due to the high cost of imported molasses substrate. Thus, the high cost of the raw materials for the production of baker's yeast has caused Saudi Arabia and many other Gulf Coast countries to rely upon importation of baker's yeast to meet demand.
Commercial baker's yeasts produced from strains of Saccharomyces cerevisiae have the following average chemical composition: 47% C, 32% O2, 6% H2, 7.7% N2, 2% K, 1.2% P, 1% S, 0.2% Mg, 0.1% Na, and other trace elements. In addition, the yeast cells contain small amounts of vitamin B complex, of which D-Pantothenic acid, D-Biotin and m-Inositol are essential because the yeast cells cannot synthesize them. These elements and compounds must be provided in the production medium in enough quantities and metabolizable forms.
Dates are known to contain a variety of simple sugars, and may contain 65-87% sugars, 1-3% proteins, in addition to many minerals important for yeast nutrition, including potassium, magnesium, sulphur, phosphorus, iron, calcium, and chlorine. Although various laboratory studies have suggested that it may be theoretically possible to use portions of or extracts from dates as a substrate for the production of baker's yeast, it has not been practical to do so industrially because it has not been shown that the process is economically efficient, i.e., the biomass of yeast produced from a given mass of substrate has not been high enough or efficient enough to justify the expenditure in raw materials for the substrate and nutrients, the labor, the capital equipment, and other costs for production, transport, and delivery to the consumer. It has been reported that the optimum biomass concentration in the fermentation medium for economical production is about 40 g/l, which existing methods and processes have not come close to.
Thus, a method of producing baker's yeast solving the aforementioned problems is desired.